Dialkyl sulfides are versatile reagents for organic syntheses. Moreover, lower dialkyl sulfides are often employed as valuable solvents. Most organic sulfides with low molecular mass have intense unpleasant odors, which in many cases is further deteriorated through the presence of sulfur-containing impurities (K. -M. Roy, “Thiols and Organic Sulfides”, Ullmann's Encyclopedia of Industrial Chemistry, 7th Ed., pages 1 to 28, Wiley-VCH Verlag GmbH & Co. KGaA 2008). For example, commercial dimethyl sulfide (DMS) contains highly malodorous impurities such as carbon disulfide, carbonyl sulfide, methyl thiol, dimethyldisulfide, hydrogen sulfide and other sulfurous compounds at low levels. Even though the concentration of these impurities is less than one percent and for some compounds is less than 200 ppm, the odor of the impurities gives the DMS a vile stench of rotten eggs, cabbage and skunk. Some sulfur compounds having the odor of garlic or onions may also contribute to the odor. DMS of high purity has the odor of corn or a grassy meadow (D. J. Rowe, Perfumer & Flavorist 1998, Vol. 23, pages 9 to 14).
DMS is used as an anti-coking agent in petroleum steamcrackers and as raw material to make the solvent dimethylsulfoxide (DMSO). DMS is also used as a solvent and for coordination to metal compounds or other Lewis acids, i.e. borane compounds. Dimethyl sulfide borane (DMSB) is a stable concentrated (10M) form of borane (BH3) utilized in the pharmaceutical industry for the reduction of carbonyl compounds, imines, and hydroboration of double bonds in alkenes or alkynes. The unpleasant odor of DMSB made from impure DMS can be noticed at very low levels in production operations and can drift in the wind into communities. Responsible companies do not want to subject employees or neighboring populations to the odor from using DMS or DMSB.
The purification of DMS has been addressed in JP 49006287 by a steam distillation process and separation of water from the dialkyl sulfide. This method is inappropriate for DMSB preparation due to residual water in the DMS.
U.S. Pat. No. 6,736,879 discloses an absorption method to remove carbon disulfide from dimethyl sulfide. The absorption media is an activated alumina treated with alkali metal and alkaline earth compounds and can be regenerated. However, absorption of the impurities in dialkyl sulfides may remove some contaminates but will not completely remove the variety of impurities due to the reversibility of the absorption process.
Some manufacturers of dimethyl sulfide and dimethyldisulfide have used odor-masking compounds to give the mixture a more pleasant odor (U.S. Pat. Nos. 5,559,271, 6,639,110). The compounds used have functional groups that are reactive with borane and therefore cannot be used in the application of DMSB preparation.
Removal of hydrogen sulfide, carbon disulfide, and thiols (collectively called acid gases) from gas streams and hydrocarbon mixtures has been tried with a number of methods, such as passing the gas through a packed bed calcinator (U.S. Pat. No. 6,136,144) or water and bromine (U.S. Pat. No. 5,433,828), absorption with nitrogen containing heterocycles (DE 19828977, U.S. Pat. No. 5,480,860) or reversible absorbents (U.S. Pat. No. 4,173,619, US 2005/0205470). Hydrocarbon purification to remove sulfurous and phosphine components prior to polymerization has used alkali metals on supports (U.S. Pat. Nos. 5,302,771, 6,124,410) or ion exchanged zeolites (U.S. Pat. No. 4,358,297). Other examples use amines on a solid support (U.S. Pat. No. 4,999,175), transition metal oxides (U.S. Pat. No. 5,157,201) or reaction with a Group 1B metal halide amine (U.S. Pat. No. 5,382,417).
Removal of alkyl sulfides and thiols in plant effluent by oxidation has been addressed (U.S. Pat. Nos. 6,015,536, 6,277,344, 5,439,641). Oxidation is not applicable to DMS purification because the DMS would also be oxidized.
High purity DMS is a desirable commercial product suitable as flavoring agent or solvent as well as low odor compounds made from it, i.e. DMSO or DMSB. Selective removal of undesirable components, while leaving the desired dimethyl sulfide, is not adequately addressed by current literature. Furthermore, oxidation methods are destructive to all components of the mixture. It is highly desirable to remove malodorous impurities from DMS while leaving the DMS unchanged.
It was therefore an object of the present invention to develop processes for the purification of dialkyl sulfides in order to provide low odor dialkyl sulfides, i.e. with an odor that is less noticeable compared to commercially available dialkyl sulfides.